Stecker Collin, Liu Zhenyu, Hieulle Jeremy, Zhang Siming, Ono Luis K, Wang Guofeng, Qi Yabing
Energy Materials and Surface Sciences Unit (EMSSU), Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States.
ACS Nano. 2021 Sep 28;15(9):14813-14821. doi: 10.1021/acsnano.1c04867. Epub 2021 Aug 17.
Metal halide perovskites (MHPs) have become a major topic of research in thin film photovoltaics due to their advantageous optoelectronic properties. These devices typically have the MHP absorber layer sandwiched between two charge selective layers (CSLs). The interfaces between the perovskite layer and these CSLs are potential areas of higher charge recombination. Understanding the nature of these interfaces is key for device improvement. Additionally, non-stoichiometric perovskite films are expected to strongly impact the interfacial properties. In this study, the interface between CHNHPbI (MAPbI) and copper phthalocyanine (CuPc), a hole transport layer (HTL), is studied at the atomic scale. We use scanning tunneling microscopy (STM) combined with density functional theory (DFT) predictions to show that CuPc deposited on MAPbX (X = I,Br) forms a self-assembled layer consistent with the α-polymorph of CuPc. Additionally, STM images show a distinctly different adsorption orientation for CuPc on non-perovskite domains of the thin film samples. These findings highlight the effect of non-stoichiometric films on the relative orientation at the MHP/HTL interface, which may affect interfacial charge transport in a device. Our work provides an atomic scale view of the MHP/CuPc interface and underscores the importance of understanding interfacial structures and the effect that the film stoichiometry can have on interfacial properties.
金属卤化物钙钛矿（MHPs）因其优异的光电性能，已成为薄膜光伏领域的一个主要研究课题。这些器件通常将MHP吸收层夹在两个电荷选择层（CSL）之间。钙钛矿层与这些CSL之间的界面是电荷复合可能性较高的潜在区域。了解这些界面的性质是改进器件的关键。此外，非化学计量比的钙钛矿薄膜预计会对界面性质产生重大影响。在本研究中，我们在原子尺度上研究了CHNHPbI（MAPbI）与作为空穴传输层（HTL）的铜酞菁（CuPc）之间的界面。我们使用扫描隧道显微镜（STM）结合密度泛函理论（DFT）预测，表明沉积在MAPbX（X = I，Br）上的CuPc形成了与CuPc的α-多晶型一致的自组装层。此外，STM图像显示了CuPc在薄膜样品的非钙钛矿区域上明显不同的吸附取向。这些发现突出了非化学计量比薄膜对MHP/HTL界面相对取向的影响，这可能会影响器件中的界面电荷传输。我们的工作提供了MHP/CuPc界面的原子尺度视图，并强调了理解界面结构以及薄膜化学计量比对界面性质影响的重要性。
